Application for the Reassessment of a Hazardous Substance under ...

activity). In fact, treatment was stopped after 20 days because the level of inhibition hadreached 30%. Following a 15-day washout period, plasma ChE activity returned topretreatment levels.Plasma ChE activity in male subjects treated with 2.5 mg/d dichlorvos―Results expressed as the mean ΔpH/h, with the % inhibition relative to pretreatment activity contained inparentheses. The range is also shown for the dichlorvos group in parentheses; 1 = average of 4measurements for each subject.―In the supplementary group of subjects treated with 1.5 mg/g dichlorvos (see Tablebelow), progressive inhibition of plasma ChE activity occurred from the second week,reaching a maximum of 41% at the end of the 60-day treatment period (relative topretreatment activity). However, the magnitude of this effect was partially negated bythe up to 24% reduction in plasma ChE activity in the concurrent controls over the sametime. When the data were corrected to account for the declining activity in the controlgroup, inhibition of plasma ChE activity in the dichlorvos subjects was 27% after 16days and continued to be depressed by 13-21% for the remainder of the dosing period.During the 74-day post-treatment period, plasma ChE activity recovered to controllevels within 2 weeks. The author indicated that over a period of approximately 3 weeks(corresponding to post-treatment days 31-48), there was a general decrease in plasmaChE activity in the performing laboratory. This was apparently remedied when a freshacid cleaning solution was employed to clean the laboratory glassware used for the ChEassay.Dichlorvos reassessment – application Page 273 of 436